BOREAS RSS-12 Automated Ground Sunphotometer Measurements in the SSA Summary The BOREAS RSS-12 team collected both ground and airborne sunphotometer measurements for use in characterizing the aerosol optical properties of the atmosphere during the BOREAS data collection activities. These measurements are to be used to: 1) measure the magnitude and variability of the aerosol optical depth in both time and space; 2) determine the optical properties of the boreal aerosols; and 3) atmospherically correct some remotely sensed data acquired during BOREAS. These data cover selected days and times from May to September 1994 and were taken from one of two ground sites near Candle Lake in the SSA. The data described in this document are from the field sunphotometer data. The data are stored in tabular ASCII files. Table of Contents * 1 Data Set Overview * 2 Investigator(s) * 3 Theory of Measurements * 4 Equipment * 5 Data Acquisition Methods * 6 Observations * 7 Data Description * 8 Data Organization * 9 Data Manipulations * 10 Errors * 11 Notes * 12 Application of the Data Set * 13 Future Modifications and Plans * 14 Software * 15 Data Access * 16 Output Products and Availability * 17 References * 18 Glossary of Terms * 19 List of Acronyms * 20 Document Information 1. Data Set Overview 1.1 Data Set Identification BOREAS RSS-12 Automated Ground Sunphotometer Measurements in the SSA 1.2 Data Set Introduction The Automated Ground Sunphotometer (AGSP) data set consists of instrument voltages; Sun position information; and ozone (O3), nitrogen dioxide (NO2) and aerosol optical depth values. These data were collected and processed by the BOReal Ecosystem-Atmosphere Study (BOREAS) Remote Sensing Science Team 12 (RSS- 12) at the National Aeronautics and Space Administration (NASA) Ames Research Center (ARC). The data provide a good characterization of atmospheric aerosols during the data collection periods. 1.3 Objective/Purpose The overall goal of this investigation was to measure aerosol optical properties from both ground- and aircraft-based sunphotometers during the BOREAS Intensive Field Campaigns (IFCs). These measurements are to be used to: 1) Measure the magnitude and variability of the aerosol optical depth in both time and space. 2) Determine the optical properties of the boreal aerosols. 3) Atmospherically correct selected remotely sensed data acquired during BOREAS. 1.4 Summary of Parameters The phenomenon being measured is the atmospheric aerosol optical depth. The parameters include Rayleigh optical depth, aerosol optical depth, time, latitude, longitude, air mass, and solar position. 1.5 Discussion The AGSP data will be used in conjunction with the Airborne Tracking Sunphotometer (ATSP) data to determine the magnitude and variability of the aerosol optical depth in both time and space. The aerosol optical depth data will be inverted using an algorithm developed by King et al., 1978, to derive the size distribution of the boreal aerosols. Mie theory will then be used to calculate the aerosol phase function and single-scattering albedo. Finally, the atmospheric correction algorithm of Wrigley et al., 1992, will be used to atmospherically correct selected NS001 Thematic Mapper (TMS), Landsat Thematic Mapper (TM), and Moderate-resolution Imaging Spectrometer (MODIS) Airborne Simulator (MAS) data collected during the 1994 BOREAS IFCs 1-3. Atmospheric correction of Landsat TM and other satellite data will use the aerosol properties derived from surface optical depth measurements. Atmospheric correction of NS001 and MAS data will use aerosol properties derived from the airborne optical depth measurements as well as those from the surface measurements. 1.6 Related Data Sets BOREAS RSS-12 Airborne Tracking Sunphotometer Measurements BOREAS RSS-11 Ground Network of Sunphotometer Measurements BOREAS RSS-18 Ground Sunphotometer Measurements in the SSA 2. Investigators 2.1 Investigators Names and Titles Robert C. Wrigley (retired 1995) Principal Investigator Co-Investigators: Michael A. Spanner Robert E. Slye Philip B. Russell John M. Livingston 2.2 Title of Investigation BOREAS Aerosol Determinations and Atmospheric Correction for BOREAS Imagery 2.3 Contact Information Contact 1 -------------------------------- Michael A. Spanner Co-Investigator Johnson Controls World Services NASA Ames Research Center Moffett Field, CA (415) 604-3620 (415) 604-4680 (fax) mspanner@gaia.arc.nasa.gov Contact 2 -------------------------------- Jaime Nickeson NASA/GSFC Greenbelt, MD (301) 286-3373 (301) 286-0239 (fax) Jaime.Nickeson@gsfc.nasa.gov 3. Theory of Measurements The instrument measures direct beam solar radiation for 10 channels in the visible and near infrared wavelengths. The solar radiation data are collected in the form of voltages. The instrument was calibrated both before and after the experiment using the Langley plot technique. For calibration, data are collected at a number of solar angles from low solar elevation (air mass = 5) to high solar elevation (air mass = 1.8). A regression is developed between log voltage and air mass. This regression equation is then extrapolated to an air mass of 0. This value, called the zero air mass intercept voltage, is the value used to calibrate of the instrument in a given channel. Great care must be taken to ensure the stability of these intercept voltages over time. A calibration history is maintained that attests to the stability of the instrument. The voltages measured by the instrument during the BOREAS IFCs were converted to total optical depth using the zero air mass intercept voltages calculated from the calibrations using the equation: V/V0 = (Rm/R)2 exp(-mt) where V is the measured voltage, V0 is the zero air mass voltage intercept, R is the radius of Earth's orbit at the time, Rm is the mean radius, m is the air mass at the time, and t is the total optical depth (usually written as the Greek letter tau). The aerosol optical depth is calculated from the total optical depth by subtracting a number of components that contribute to the total optical depth: Rayleigh scattering and gaseous absorption due to ozone and NO2. The Rayleigh optical depth is calculated using pressure measured on the aircraft. NO2 and ozone optical depths are subtracted from the total minus Rayleigh optical depth to obtain the aerosol optical depth. NO2 abundance is obtained from climatology tables based on Noxon, 1979, and convolved with absorption coefficients at field sunphotometer wavelengths. Ozone optical depth is calculated using ozone abundances from the Total Ozone Mapping Spectrometer (TOMS) satellite instrument and convolved with absorption coefficients at the field sunphotometer wavelengths. The result of this processing is the aerosol optical depth measured in nine channels (not including the 940 nm water vapor channel) at approximately 1-minute intervals on the ground. The correction of remote sensing data acquired from satellites or aircraft for effects due to the intervening atmosphere has proven to be a difficult problem. Not only does the atmosphere reduce the transmission of the incoming, reflected, and emitted radiation, but it contributes reflected and emitted radiation of its own. Under high aerosol concentration conditions, atmospheric radiation comprises over 90% of the satellite observed radiance, but even much smaller effects would degrade the quantitative use of these data unless they are taken into account. The interaction of radiation with the atmosphere is complex and has proved difficult to calculate without reference to measurements made at, or close to, the time and location of interest. Effects due to Rayleigh scattering from atmospheric gases are well understood because the major gases (nitrogen, oxygen) that comprise 99% of the atmosphere are well mixed and their concentrations with altitude are known. The effects due to small particle (aerosol) scattering are quite variable because of the wide range of aerosol concentrations and the variety of aerosols found in the atmosphere. Because aerosol concentrations cannot be known a priori, they must be measured at the time and location of remote sensing data acquisition. The physical properties of aerosols such as size, shape, refractive index, and concentration in the atmosphere control the aerosol interaction with light according to a set of optical properties. Three fundamental properties are (1) the aerosol optical depth, an indirect measure of the size and number of particles present in a given column of air; (2) the single scattering albedo, the fraction of light intercepted and scattered by a single particle; and (3) the phase function, a measure of the light scattered by a particle as a function of angle with respect to the original direction of propagation. 4. Equipment 4.1 Sensor/Instrument Description The automated solar radiometer instrument consists of a 10-channel solar radiometer, solar-tracking mount, and data acquisition/controller box with tracking and temperature control. 4.1.1 Collection Environment The data collection took place at either the Sandy Bay Campground site (main site) or the parking lot at the Ship’s Lantern Hotel, both in Candle Lake, Saskatchewan. Data were taken to coincide with NASA C-130 flights where airborne sunphotometer measurements were being taken. Ground measurements were more frequent than aircraft flights however. The field sunphotometer collected data on 52 days between 25-May-1994 and 19-Sep-1994. 4.1.2 Source/Platform The instrument is mounted on a short tripod that rests on the ground. 4.1.3 Source/Platform Mission Objectives The AGSP was developed to obtain accurate multispectral atmospheric extinction measurements in the field for the overall purpose of atmospheric correction of remotely sensed data. 4.1.4 Key Variables The primary quantity being measured is the total optical depth. The aerosol optical depth is derived by subtracting optical depths caused by other components of the atmosphere: Rayleigh scattering, ozone absorption, and NO2 absorption. 4.1.5 Principles of Operation The instrument measures energy in the direct beam of the Sun. From the calibrations developed before and after the experiment, these voltages are converted to aerosol optical depth, which is a measure of the extinction of the direct solar beam by aerosols and particulates in the atmosphere. 4.1.6 Sensor/Instrument Measurement Geometry The field sunphotometer has a 2.0 degree field of view (FOV) and is heated to 44 °C to maintain temperature stability. It has 10 filters. The nominal wavelengths and the full width half maximum (FWHM) for the instrument are presented in the following table. Wavelength (nm) FWHM (nm) --------------- --------- 380.2 11.7 401.1 10.2 438.6 10.6 521.6 11.6 608.5 10.2 666.9 10.6 779.3 10.1 865.6 12.6 939.8 11.6 1027.1 7.4 4.1.7 Manufacturer of Sensor/Instrument Dr. John Reagan Department of Electrical and Computer Engineering University of Arizona Tucson, AZ (520)621-6203 4.2 Calibration 4.2.1 Specifications Factors that may affect calibration are instrument variations that may occur between calibrations. Significant drifts in calibration during the time period of the experiment were not observed. 4.2.1.1 Tolerance The aerosol optical depths are accurate to the uncertainties given with the data. 4.2.2 Frequency of Calibration The instrument was calibrated at the Mt. Lemmon Steward Observatory, Tucson, AZ, in April 1994 (before the field season) and at the Mauna Loa Observatory, HO, in November 1994 (after the field season). 4.2.3 Other Calibration Information 5. Data Acquisition Methods The instrument is initialized through the controller box and then a solar radiometer telescope is manually aligned with the solar image in the crosshairs. Once the telescope is aligned, the automated solar radiometer will collect data at the selected time interval by first tracking the Sun, then reading the output of all 10 channels, temperature, and the time of data collection. The time interval used for BOREAS was 1-minute. After each data collection sequence, the solar radiometer telescope is stepped away from direct solar alignment to reduce solar exposure on the interference filters. The data collection continues until the final stop time is reached or data collection is terminated. At this point, the instrument turns off the heating elements and is ready to transmit data to a computer through the RS232 port. The instrument has nonvolatile memory. 6. Observations 6.1 Data Notes None given. 6.2 Field Notes The field sunphotometer operator normally takes notes of significant events while the instrument is acquiring data. These notes supplement the data file of detector voltages or optical depths and permit determination of the presence of variable cloud interference with remote sensing data collection. The notes, if any, help identify data problems during processing. Anyone interested in these notes should contact RSS-12 personnel at NASA ARC. 7. Data Description 7.1 Spatial Characteristics The field sunphotometer views the Sun with a 2-degree FOV and typically acquires data every minute during operation. The system is not moved during a collection period, which was about 4 hours at the main site, Sandy Bay. A collection period is a continuous data acquisition cycle. 7.1.1 Spatial Coverage The field sunphotometer was operated from two locations in the Southern Study Area (SSA): Ship's Lantern Hotel and Sandy Bay Campground. BORIS (X,Y) UTM (E,N) Latitude,Longitude ------------- ------------------ -------------------- Ship’s Lantern Hotel 377.02,321.47 481967.2,5955747.4 53.75005 N, 105.27347 W Sandy Bay Campground 372.84,326.53 478233.5,5961137.1 53.79835 N, 105.33047 W The NAD83 corner coordinates of the SSA are: Latitude Longitude -------- --------- Northwest 54.321 N 106.228 W Northeast 54.225 N 104.237 W Southwest 53.515 N 106.321 W Southeast 53.420 N 104.368 W 7.1.2 Spatial Coverage Map Not available. 7.1.3 Spatial Resolution The field sunphotometer views the Sun with a 2-degree FOV. 7.1.4 Projection Not applicable. 7.1.5 Grid Description Not applicable. 7.2 Temporal Characteristics 7.2.1 Temporal Coverage The AGSP typically acquires data once every minute during operation. The system was not moved during a collection period. Data were acquired during three IFCs in 1994. The data were intended to be coincident with the aircraft and satellite overpasses. The days, times, and locations were: Date Time (UTC) Location ----------- ----------------- --------- 25-May-1994 15:55:09-21:31:09 Sandy Bay 26-May-1994 15:13:17-19:00:13 Sandy Bay 27-May-1994 14:30:07-20:00:13 Sandy Bay 29-May-1994 14:27:08-18:50:08 Sandy Bay 31-May-1994 14:41:09-21:00:08 Sandy Bay 31-May-1994 11:42:11-13:13:08 Ship's Lantern 01-Jun-1994 14:19:10-21:00:09 Sandy Bay 04-Jun-1994 13:50:10-21:00:10 Sandy Bay 06-Jun-1994 15:17:08-19:00:10 Sandy Bay 06-Jun-1994 12:15:09-14:40:20 Ship's Lantern 07-Jun-1994 12:03:07-21:00:10 Ship's Lantern 08-Jun-1994 15:00:09-17:45:08 Sandy Bay 10-Jun-1994 12:02:13-16:35:08 Ship's Lantern 11-Jun-1994 15:51:08-19:00:19 Sandy Bay 11-Jun-1994 12:10:09-12:40:07 Ship's Lantern 20-Jul-1994 15:52:05-21:00:10 Sandy Bay 21-Jul-1994 15:35:11-22:30:08 Sandy Bay 21-Jul-1994 12:04:10-15:00:10 Ship's Lantern 22-Jul-1994 15:31:09-17:30:10 Ship's Lantern 23-Jul-1994 15:40:08-19:00:11 Sandy Bay 23-Jul-1994 11:58:09-14:40:09 Ship's Lantern 24-Jul-1994 15:30:08-21:30:10 Sandy Bay 24-Jul-1994 12:03:12-14:41:08 Ship's Lantern 25-Jul-1994 15:31:09-22:30:21 Sandy Bay 25-Jul-1994 12:12:11-14:39:12 Ship's Lantern 26-Jul-1994 15:43:10-19:00:10 Sandy Bay 27-Jul-1994 15:22:10-22:20:10 Sandy Bay 28-Jul-1994 16:09:09-19:00:09 Sandy Bay 30-Jul-1994 15:30:11-21:00:10 Sandy Bay 31-Jul-1994 15:36:11-19:00:14 Sandy Bay 01-Aug-1994 16:40:11-19:00:10 Sandy Bay 02-Aug-1994 15:47:12-20:22:12 Sandy Bay 04-Aug-1994 19:10:11-23:00:09 Sandy Bay 31-Aug-1994 18:38:05-22:00:09 Sandy Bay 01-Sep-1994 15:27:04-23:00:09 Sandy Bay 01-Sep-1994 13:04:09-14:45:09 Ship's Lantern 02-Sep-1994 15:30:04-23:00:09 Sandy Bay 02-Sep-1994 12:40:10-14:45:08 Ship's Lantern 05-Sep-1994 15:25:03-22:02:12 Sandy Bay 05-Sep-1994 12:45:07-14:44:08 Ship's Lantern 06-Sep-1994 15:22:03-23:00:09 Sandy Bay 06-Sep-1994 12:43:09-14:45:08 Ship's Lantern 07-Sep-1994 15:44:04-22:31:08 Sandy Bay 07-Sep-1994 12:54:09-14:30:08 Ship's Lantern 12-Sep-1994 17:06:05-20:06:03 Sandy Bay 13-Sep-1994 13:21:07-22:00:09 Sandy Bay 14-Sep-1994 18:35:06-19:26:09 Sandy Bay 15-Sep-1994 19:43:04-23:00:08 Sandy Bay 16-Sep-1994 13:35:04-23:00:19 Sandy Bay 17-Sep-1994 13:35:03-23:00:08 Sandy Bay 18-Sep-1994 13:31:05-23:00:18 Sandy Bay 19-Sep-1994 13:44:04-22:30:09 Sandy Bay 7.2.2 Temporal Coverage Map Not available. 7.2.3 Temporal Resolution The AGSP typically acquires data once every minute during operation. The data collection itself normally takes 10 or 15 seconds, dominated primarily by the time needed to re-point the instrument for solar tracking. 7.3 Data Characteristics Data characteristics are defined in the companion data definition file (r12sunpd.def). 7.4 Sample Data Record Sample data format shown in the companion data definition file (r12sunpd.def). 8. Data Organization 8.1 Data Granularity All of the Automated Ground Sunphotometer Measurements in the SSA Data are contained in one dataset. 8.2 Data Format(s) The data files contain numerical and character fields of varying length separated by commas. The character fields are enclosed with a single apostrophe marks. There are no spaces between the fields. Sample data records are shown in the companion data definition files (r12sunpd.def). 9. Data Manipulations 9.1 Formulae For all sunphotometer channels except the 940 nm, the Bouguer-Lambert-Beer extinction law was used to describe the attenuation of solar radiation: V = (R'/R)2 V0 exp(-m tau) = V'0 exp(-m tau) where V is the output voltage of the detector at a given wavelength, V0 is the zero air-mass voltage intercept at that wavelength for the mean Earth-Sun separation R', R is the Earth-Sun separation at the time of observation, m is the atmospheric air mass between the instrument and the sun, tau is the wavelength-dependent total vertical optical depth above the sunphotometer, and V'0 is the zero-air-mass voltage intercept for the Earth-Sun separation R at the time of observation. The 940-nm channel requires different processing and is not included this data set. The logarithm of the above equation, ln V = ln V'0 - m tau, is used in calibration to provide the V'0 values for each channel (i.e., zero air mass Langley plot intercept voltages). When the detector voltages are plotted against the air mass, the intercept is the V'0. After calibration, this equation can be solved for tau to provide the total optical depth. The total optical depth is then decomposed using tau = tau_r + tau_a + tau_O3 + tau_NO2 + tau_H2O, where these terms are the optical depth due to Rayleigh scattering, aerosols, ozone, NO2, and water vapor, respectively. The source for each of these terms is given in Section 7.3. Water vapor was ignored because it contributes only in the 940-nm channel. This description is taken from Spanner et al., 1990, where more information concerning the data processing can be found. 9.1.1 Derivation Techniques and Algorithms Description of algorithms can be found in Spanner et al., 1990. 9.2 Data Processing Sequence 9.2.1 Processing Steps The steps for processing are as follows: 1) acquire the data; 2) transfer data to computer; 3) run program to reformat data; 4) run a program to calculate all the variables, including solar zenith angle, air mass, Rayleigh optical depth, and instantaneous optical depth (total optical depth minus Rayleigh optical depth); 5) calculate NO2 and ozone optical depths from Noxon et al., 1979, and TOMS data, respectively; and 6) subtract NO2 and ozone to derive aerosol optical depth. The ozone abundance was determined from the TOMS satellite instrument convolved with ozone absorption coefficients from Penney (1979). The following table shows the values calculated for NO2 and ozone optical depth, which were subtracted from the instantaneous optical depth to derive the aerosol optical depth. Wavelength NO2 Tau Ozone Tau 380 0.003 0.000 401 0.003 0.000 439 0.002 0.001 522 0.001 0.015 608 0.0 0.041 667 0.0 0.014 779 0.0 0.002 866 0.0 0.001 1027 0.0 0.0 9.2.2 Processing Changes The processing sequence has not changed over time. 9.3 Calculations 9.3.1 Special Corrections/Adjustments No special corrections or adjustments have been made. 9.3.2 Calculated Variables Description of algorithms can be found in Spanner et al., 1990. 9.4 Graphs and Plots Plots have been provided to BORIS and can be made available upon request. 10. Errors 10.1 Sources of Error Calibration errors are the main source of error in the derivation of aerosol optical depth. 10.2 Quality Assessment 10.2.1 Data Validation by Source Data were compared with the RSS-11 ATSP measurements (see related data sets, Section 1.6). 10.2.2 Confidence Level/Accuracy Judgment The data are of high quality, because a good calibration of the instrument was performed before and after the BOREAS field collection effort. However, post- BOREAS calibration data were not available for the 1027-nm channel. 10.2.3 Measurement Error for Parameters Uncertainties for the aerosol optical depths were determined by using uncertainty propagation through the algorithm. The aerosol optical depth uncertainty is dependent on the uncertainty in the Rayleigh, ozone, and NO2 optical depths, as well as the uncertainty in the intercept voltage (calibration error), instantaneous measurement, and airmass. Aerosol optical depth uncertainties are given in the data files and are summarized in Section 7.3 of this document. 10.2.4 Additional Quality Assessments None. 10.2.5 Data Verification by Data Center Visual review and use of selected subsets of the data have shown them to be of good quality with no noteworthy problems. 11. Notes 11.1 Limitations of the Data 11.2 Known Problems with the Data Because the post-BOREAS calibration in November 1994 did not provide intercept voltage data for the 1027-nm channel, an updated voltage was not available. An estimate based on previous calibrations was used. 11.3 Usage Guidance The values of aerosol optical depth are accurate instantaneous values of aerosol optical depth. These data were taken every minute; therefore, under conditions of rapid variability in cloudiness or haze, the data may not be internally consistent or appropriate. It is useful to calculate averages of aerosol optical depth over periods of time (for example, 30-minutes) to get a more accurate measure of the average conditions at a site. 11.4 Other Relevant Information The aerosol optical depth at 940 nm was not calculated because this channel primarily measures absorption due to water vapor. 12. Application of the Data Set These data can be used for correcting various visible and infrared satellite and aircraft image products or for characterizing the atmospheric aerosols at the times of the flights. 13. Future Modifications and Plans None. 14. Software 14.1 Software Description NASA ARC software was developed in FORTRAN on a VAX to implement the data processing procedure described in Section 9.1. Input data include sunphotometer data files as well as ozone and NO2 optical depth parameters. Aerosol optical depths were calculated and written to the data files. No special software is needed to read the data files because they are stored comma delimited. 14.2 Software Access This software is used to generate the data product from the detector voltages and is not needed to use the data. 15. Data Access 15.1 Contact Information Ms. Beth Nelson BOREAS Data Manager NASA GSFC Greenbelt, MD (301) 286-4005 (301) 286-0239 (fax) beth@ltpmail.gsfc.nasa.gov 15.2 Data Center Identification See Section 15.1 15.3 Procedures for Obtaining Data Users may place requests by telephone, electronic mail, or fax. 15.4 Data Center Status/Plans The RSS-12 ground sunphotometer data are available from the Earth Observing System Data and Information System (EOSDIS), Oak Ridge National Laboratory (ORNL), Distributed Active Archive Center (DAAC). The BOREAS contact at ORNL is: ORNL DAAC User Services Oak Ridge National Laboratory Oak Ridge, TN (423) 241-3952 ornldaac@ornl.gov ornl@eos.nasa.gov 16. Output Products and Availability 16.1 Tape Products None. 16.2 Film Products None. 16.3 Other Products The data are available as tabular ASCII files. 17. References 17.1 Platform/Sensor/Instrument/Data Processing Documentation Portable Radiometer Data Reduction Manual for use with PDATA7. 17.2 Journal Articles and Study Reports Bruegge, C.J., R.N. Halthore, B. Markham, M. Spanner, and R. Wrigley. 1992. Aerosol optical depth retrievals over the Konza prairie. Journal of Geophysical Research 97(D17):18743-18758. King, M., D. Bryne, B. Herman, and J. Reagan. 1978. Aerosol size distributions obtained by inversion of spectral optical depth measurements. J. Atmos. Sci. 35:2153-2167. Noxon, J. 1979. Stratospheric NO2, 2, Global behavior, J. Geophys. Res. 84:5067- 5076. Penney, C.M. 1979. Study of temperature dependence of the Chappuis band absorption of ozone, NASA Contract Rep. 158977, General Electric Company, Schenectady, N.Y. Russell, P., J. Livingston, E. Dutton, R. Pueschel, J. Reagan, T. DeFoor, M. Box, D. Allen, P. Pilewskie, B. Herman, S. Kinne and D. Hofmann. 1994. Pinatubo and pre-Pinatubo optical depth spectra: Mauna Loa measurements, comparisons, inferred particle size distributions, radiative effects, and relationship to lidar data. J. Geophys. Res. 98:22,969-22,985. Sellers, P., and F. Hall. 1994. Boreal Ecosystem-Atmosphere Study: Experiment Plan. Version 1994-3.0, NASA BOREAS Report (EXPLAN 94). Sellers, P., and F. Hall. 1996. Boreal Ecosystem-Atmosphere Study: Experiment Plan. Version 1996-2.0, NASA BOREAS Report (EXPLAN 96). Sellers, P., F. Hall, and K.F. Huemmrich. 1996. Boreal Ecosystem-Atmosphere Study: 1994 Operations. NASA BOREAS Report (OPS DOC 94). Sellers, P., F. Hall, and K.F. Huemmrich. 1997. Boreal Ecosystem-Atmosphere Study: 1996 Operations. NASA BOREAS Report (OPS DOC 96). Sellers, P., F. Hall, H. Margolis, B. Kelly, D. Baldocchi, G. den Hartog, J. Cihlar, M.G. Ryan, B. Goodison, P. Crill, K.J.Ranson, D. Lettenmaier, and D.E. Wickland. 1995. The boreal ecosystem-atmosphere study (BOREAS): an overview and early results from the 1994 field year. Bulletin of the American Meteorological Society. 76(9):1549-1577. Sellers, P., and F. Hall. 1997. BOREAS Overview Paper. JGR Special Issue (in press). Spanner, M., R. Wrigley, R. Pueschel, J. Livingston, and D. Colburn. 1990. Determination of atmospheric optical properties for the First ISLSCP Field Experiment (FIFE). Journal of Spacecraft and Rockets 27:373-379. Wrigley, R.C., M.A. Spanner, R.E. Slye, R.F. Pueschel, and H.R. Aggarwal. 1992. Atmospheric correction of remotely sensed image data by a simplified model. Journal of Geophysical Research 97(D17):18797-18814. Young, A. 1980. Revised depolarization corrections for atmospheric extinction. Applied Optics 19:3427-3428. 17.3 Archive/DBMS Usage Documentation 18. Glossary of Terms air mass - secant of the solar zenith angle optical depth - an indirect measure of the size and number of particles present in a given column of air, which is a measure of the extinction of the direct solar beam by aerosols and particulates in the atmosphere, or by scattering. Also referred to as optical thickness. phase function - a measure of the light scattered by a particle as a function of angle with respect to the original direction of propagation radiometer - an instrument for measuring radiant energy Rayleigh - wavelength-dependent scattering directly proportional scattering to (1 + cos2 angle) and indirectly proportional to wavelength4 single - the fraction of light intercepted and scattered by a scattering single particle albedo 19. List of Acronyms AGSP - Automated Ground Sunphotometer ARC - Ames Research Center ATSP - Airborne Tracking Sunphotometer BOREAS - BOReal Ecosystem-Atmosphere Study BORIS - BOReas Information System DAAC - Distributed Active Archive Center EOS - Earth Observing System EOSDIS - EOS Data and Information System FIFE - First ISLSCP Field Experiment FOV - Field of View FWHM - Full Width Half Maximum GMT - Greenwich Mean Time GSFC - Goddard Space Flight Center IFC - Intensive Field Campaign ISLSCP - International Satellite Land Surface Climatology MAS - MODIS Airborne Simulator MODIS - MODerate-resolution Imaging Spectrometer NASA - National Aeronautics and Space Administration NSA - Northern Study Area ORNL - Oak Ridge National Laboratory PANP - Prince Albert National Park RSS-12 - Remote Sensing Science Team 12 SSA - Southern Study Area TM - Thematic Mapper TMS - Thematic Mapper Simulator TOMS - Total Ozone Mapping Spectrometer URL - Uniform Resource Locator UTC - Universal Time Code 20. Document Information 20.1 Document Revision Dates Written: 07-Jan-1997 Last Updated: 04-May-1998 20.2 Document Review Dates BORIS Review: 19-May-1997 Science Review: 27-Jun-1997 20.3 Document ID 20.4 Citation Please acknowledge the NASA ARC investigation (RSS-12) and Robert Wrigley, Principal Investigator, if these data are used or referenced. If appropriate, the references cited in Section 17 may be used. 20.5 Document Curator 20.6 Document URL Keywords Aerosols Optical Depth Ozone RSS12_Grnd_Sunphoto.doc 05/26/98